Charles Thomson's Description of His Design
for the Great Seal of the United States  June 1782

Text of above description for the front of the Seal:

On a field Chevrons composed of seven pieces on one side & six on the other, joined together at the top in such wise that each of the six bears against or is supported by & supports two of the opposite side the pieces of the chevrons on each side alternate red & white. The shield born on the breast of an American Eagle on the wing & rising proper. In the dexter talon of the Eagle an Olive branch & in the sinister a bundle of Arrows. Over the head of the Eagle a Constellation of Stars surrounded with bright rays and at a little distance clouds.

Motto In the bill of the Eagle a scroll with these words E pluribus unum. 

Thomson obviously gave a lot of consideration to the shield design, introducing the theme of mutual support that led William Barton to suggest the 13 vertical stripes (states) supporting a chief (federal government) for the final shield. Also, based on Barton's advice, the eagle's stance was changed to "displayed," with wing tips up like we see today.

The origin of chevrons comes from a pair of rafters meeting at the peak of a house.